We have obtained evidence that vasopressin opens independent pathways for the movement of water and solutes (notably urea) across the luminal membrane of the toad bladder epithelial cell. A number of agents, including phloretin, chromate and permanganate, block vasopressin-stimulated urea transport with no effect on osmotic water flow; several anesthetic agents (methoxyflurane, halothane and methohexital) have the opposite action: inhibition of water flow with no effect on urea transport. Moreover, the anesthetic agents act at a step prior to the generation of cyclic AMP, indicating that separate adenylate cyclase-cyclic AMP systems control water and urea movement in this tissue. The anesthetic agents also block the aggregation of intramembranous particles that normally takes place following vasopressin, as revealed by the freeze-fracture technique. We plan, as a major project, a study of the two cyclic AMP-mediated pathways involved in water and urea transport, in which intracellular cyclic AMP levels, adenylate cyclase activity and binding of vasopressin to receptor sites will be determined in the presence of specific inhibitors of water (the anesthetics) or urea transport (methylene blue). We will then turn our attention to the oxidizing agents chromate and permanganate, which irreversibly inhibit urea transport at the level of the luminal membrane. We will determine whether chromate and permanganate act on a cyclic AMP-activated kinase or phosphatase involved in urea transport. Another aspect of the "two pathways" project will be a study of C14 urea movement across the epithelial cell by a special technique for the radioautography of water-soluble compounds. A broad survey of the control of water and solute transport across other epithelial cells has been started, with our findings in the toad bladder as a model. Finally, the important clues regarding hormonal transformation of the cell membrane which have been obtained with the freeze-fracture technique will be extended.